Little Carb Help?

[dhendriksen]

So I’ve got what I believe is a 2100 on my 302, and for the most part if runs great! There’s a couple of little things I’m trying to solve though.

The first that I’m hoping you all can help me with, is what I believe is the high idle and the choke. Here is how the choke plate is when the motor is cold. It physically won’t close more than this. Is this adjusted using the choke timing screw? Or is this a screw on the bottom of the carb under the diaphragm? Or somewhere else? You can see the vacuum diaphragm never has a chance to touching the choke - they’re a long ways apart.

PIC1 (choke): https://photos.app.goo.gl/4TfraPch4K1n6nHM9
PIC2 (driver side): https://photos.app.goo.gl/AtgvkhM3SmMUcNCc8

The issue I’m having is the engine fires RIGHT UP, but until it’s warm it will just die. The high idle isn’t set is my guess. I’m hoping if I can figure out how to get the choke to actually close, that I can then move on to adjusting the high idle.

Why did they have to make these adjustments so small and difficult to get to? LOL. Any pointers you can provide would be amazing.

 

[MarsChariot]

These two documents may get you going in the right direction. If not there are plenty more detailed instructions we can dig up.

 

[73azbronco]

You actually move the big black cap to adjust choke, looks electric.

 

[dhendriksen]

You actually move the big black cap to adjust choke, looks electric.

Here’s a pic of the black cap - it’s not electric. Turning this, as I understand it, will adjust how long the choke process takes…how warm it needs to get before the choke is off, by adjusting the spring tension. But that adjustment isn’t what would control how far the choke would close, would it? I mean…I guess it could by putting a ton of tension on it, but the linkage is physically hitting something that stops it dead. It’s not just under pressure from the choke timing spring. I hope that makes sense.

Pic of choke: https://photos.app.goo.gl/iFTE887V4oUDCmeu7

 

[DirtDonk]

First of all, when you are checking how far the choke plate is closed, are you opening the throttle by hand?
If not, try it again with the throttle partially open and try to push the plate closed.
There is a point that it won’t go beyond until the throttle is partially opened.

And check your ignition because, as Jacobs used to say, “because 90% of carburetor problems are ignition related“ check your ignition tune.
Check your timing, points gap and dwell (unless you’re running electronic), vacuum advance and mechanical advance actions, etc.
What ignition are you running?

 

[dhendriksen]

The ignition is standard issue cap and rotor.

 

[dhendriksen]

And yes - I tried with the throttle manually opened as well.

 

[MarsChariot]

Have you removed the air horn recently? If so, there is a small slider seal where the choke control rod passes through the air horn body and sometimes that can get rotated when putting the air horn back on. When it does get roated or just stuck with gum, it can prevent the choke rod from swinging through its required motion and the choke plate won't move.

 

[DirtDonk]

The ignition is standard issue cap and rotor.

Standard issue for what year? Points, or electronic?
If the carb is original style, then assuming this is a 72 or earlier bronco, then it is points, or at least used to be.
If it’s still standard points, then that’s all the more reason to give it a tuneup.
Yes, I realize this is a discussion about the carburetor and the choke, but without the ignition system being in top form, many of the potential benefits of adjustments and tweaks to the carburetor will go unrealized.

So, if you haven’t checked the ignition tune, might as well do it, even though you know that there is something wrong with the choke.
When you say it won’t idle when cold, sometimes that’s a tuneup issue and you could’ve had this choke issue all along.

When it’s fully warmed, does it idle at the normal speed?
Do you have a tachometer to verify idle speed?

 

[dhendriksen]

Thank you. I do have a tachometer, and it is points. The ignition components are fairly new. When it’s warm, it does idle great…but a little high. Once in a while there will be a bump/hiccup at idle but just makes the RPMs bounce for a second.

The plug wires are getting old and I’ll replace those soon.

 

[m_m70]

So has this always been an issue or is it a new problem??

The throttle has to open before the plate will close....which is why you have to pump the throttle for the choke to activate on a cold engine.

Try putting pressure on the choke plate (to close the plate) while opening up the throttle all the way and see what you feel.

 

[Oldtimer]

Take this screw (and washer) out and pull lever of of choke plate.
Is choke plate free to rotate?
Is rod free to move down & up?
You may need to pull choke control (black cap) to find the bind?

This diaphram is a choke unloader, to OPEN the choke under some prescribe conditions (can't remember what).

 

[DirtDonk]

This diaphram is a choke unloader, to OPEN the choke under some prescribe conditions (can't remember what).

Became the choke “pull-off” in a separate module on later versions.
Engine vacuum pulls the lever virtually as soon as you start cranking the engine.
Certainly as soon as it fires up.

The spring closes the choke plate fully, or almost fully, then the pull-off opens it just the correct amount, as Oldtimer was saying, to let the engine run smoothly immediately after starting while cold.

 

[dhendriksen]

So has this always been an issue or is it a new problem??

The throttle has to open before the plate will close....which is why you have to pump the throttle for the choke to activate on a cold engine.

Try putting pressure on the choke plate (to close the plate) while opening up the throttle all the way and see what you feel.

Thank you. Bronco is new to me, and was in storage for a decade, so no idea how long the problem persisted.

I’ll try a couple of these things are post a video. Thank you again.

 

[dhendriksen]

So…I got the choke adjusted and I think I’ve fixed that problem. Got the high idle adjusted along with the auto choke tension/timing. I’ve got to let it get cold again and validate, but I think we’re good.

The next thing I need to dial in is a little bit of a rough idle and what seems to be a backfire when the engine is under load but not getting throttle (IE: coasting down a hill in gear). Separate thread on that, as that feels like timing/ignition.